Magnetic heads are used in the data storage industry for reading and recording data onto narrow tracks on a magnetic medium. In a hard disc drive, a thin film magnetic head can be mounted to a head-gimbal-assembly, which can be used to position the head over concentric data tracks on the disc surface. Thin film magnetic heads can use transducer elements to detect resistance variations due to changes in an external magnetic medium. Examples of thin film magnetic heads include soft adjacent layer heads, giant magnetoresistive heads, and spin valve sensor heads.
After a magnetic head is fabricated, it is usually tested to ensure proper operability. Only magnetic heads that are found to be operational during these tests are used in the manufacturing of the hard disc drive. To test the magnetic heads, preamplifier can be used to amplify the signals that originate in the magnetic heads. During the magnetic head testing, however, the resistance or impedance of the preamplifier and the testing circuit can adversely effect the measurement of the magnetic head. For example, the impedance and resistance of the preamplifier, the magnetic head, and the connection between the head and the preamplifier can change the absolute gain and frequency response characteristics of the resulting output signal. The effect on the absolute gain level can cause amplitude test readings to be off by approximately 10-50% based on different head reader resistances for current giant magnetoresistive heads. The changes in frequency response can also effect amplitude readings at different frequency points as well as overall head performance because of a roll-off at higher frequencies.
The present invention provides a method and system for adjusting an output signal from a hard disc drive head testing device.
In one aspect of this invention, a method for testing a disc drive head usable with a disc drive head testing device is presented. The steps for this method include determining an unknown electrical property of the head testing device. This is done by generating output signals at the output stage by consecutively coupling to the input lead each test devices having known electrical properties and generating an output signal characteristic of the known electrical properties of the test devices and the unknown electrical property of the head testing device. The testing device property is then computed by solving for the unknown electrical property based on the output signals generated for each of the known test devices. For each disc drive head under test, the head is coupled to the input lead. The head is then exposed to a stored magnetic data pattern to generate a read signal at the input lead. A read output signal is generated at the output stage based on the read signal applied to the input lead by the head. The electrical property of the head under test is measured, with the measured property differing for different disc drive heads. The difference affects the generated read output signal. The read output signal is adjusted based on the testing device property and the measured property to compensate for differences in the measured property.
Each output signal can include a frequency-dependent signal, and generating the output signal comprises generating over a range of frequencies. The step of generating an output signal further comprises generating based on a frequency-variable voltage source providing a known voltage signal over the range of different electrical frequencies. The known electrical properties of each known test device can include a resistance. The unknown electrical property of the head testing device can include an impedance. The measured property can include a resistance of the drive head under test.
The step of adjusting the read output signal can include scaling the read output signal in proportion to             Rmr      +      Rin              Rcal      +      Rin        ,
where Rmr is the measured property, Rin is the computed testing device property, and Rcal is a value of a calibration device coupled to the input lead to calibrate the head test device. The output stage can include an amplifier having an adjustable amplification boost and the method can further include adjusting the amplification boost based on the measured property. The step of adjusting the amplification boost can include selecting amplification boost settings for different ranges of the measured property, the different amplification boost settings being selected to provide a similar output characteristic for different measured properties. The similar output characteristic can include a shape of a plotted output signal. The step of generating output signals can include generating a plurality of output signals using a signal generator. The method can further include determining whether the disc drive head is operational based on the adjusted read output signal.
In another aspect of this invention, a disk drive head testing apparatus includes an input lead configured for attachment to a disk drive head under test. The apparatus also includes an output stage operatively coupled to the input lead and configured to generate an output signal based on a signal received at the input lead. In addition, the apparatus includes circuitry configured to adjust the amplified output signal of the output stage based on an impedance of the testing apparatus and a resistance of a disk drive head coupled to the input lead. The apparatus can include circuitry configured to compensate the output signal to reduce gain variations due to variations in resistance of different disk drive heads coupled to the input leads. The gain variations can result from a coupling of the frequency-dependent impedance of the output stage and resistance of disk drive heads attached to the input lead. Each output signal can include a frequency-dependent signal, with the generation of the output signal over a range of frequencies.
The read output signal can be adjusted by scaling the read output signal in proportion to             Rmr      +      Rin              Rcal      +      Rin        ,
where Rmr is the measured property, Rin is the computed testing device property, and Rcal is a value of a calibration device coupled to the input lead to calibrate the head test device. The output stage can additionally include a preamplifier having an adjustable amplification boost. The amplification boost can be adjusted based on the measured property. The amplification boost can include amplification boost settings for different ranges of the measured property, the different amplification boost settings can be selected to provide a similar output characteristic for different measured properties.
In another aspect of the invention, a disk drive head testing apparatus is presented. The apparatus includes an input lead configured for attachment to a disc drive head under test and an output stage operatively coupled to the input lead and configured to generate an output signal, and means to adjust the output signal based on a known testing device property and a measured testing device property to compensate for differences in the measured property.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Implementations can provide advantages such as improved accuracy in testing the magnetic head after fabrication.